Effect of Nb content on thermal stability, mechanical and corrosion behaviors of hypoeutectic CoCrFeNiNb chi high-entropy alloys

A hypoeutectic CoCrFeNiNb chi system was synthesized to investigate the effect of Nb content on the thermal stability, mechanical properties, and corrosion behaviors. The hypoeutectic CoCrFeNiNb chi alloy, which contained the Laves phase, possessed two-phase eutectic structures. The elevated temperature may have an impact on the stability of the Laves phase. Nano-indentation measurements showed that the Laves phase is much harder than the FCC phase, which could be confirmed by the shallower maximum penetration depth in the typical P-h curve. Furthermore, the plasticity of the Laves phase was characterized by nanoindentation measurements. Compared with the FCC phase, the activation energy of dislocation nucleation in the Laves phase is much higher due to the large atomic size difference and the phase difference. Corrosion and passivation behaviors of CoCrFeNiNb chi were investigated in 3.5% NaCl solution. All the alloys exhibited spontaneous passivity and low current densities in 3.5% NaCl solution. Furthermore, the corrosion potential increased with the increasing Nb content, which indicated that the corrosion resistance enhanced with a higher Nb content.